The present invention relates to a method and apparatus for adjusting the trim on a powerboat. More particularly, the present invention relates to a method and apparatus for adjusting the trim on a powerboat that is powered by an outboard motor.
Most powerboats on the marketplace today include a trim system which allows the operator to adjust the angle of attack of the boat relative to the water. Such powerboats are generally stern driven powerboats which include outboard, stern drive, jet drive, and inboard driven boats. Adjustment of the trim system is usually accomplished by means of a hydraulic actuator which adjusts the angle of the motor relative to the boat. Normally, the maximum boat speed is attained with the outdrive trimmed "out", so that the direction of thrust creates a bow-lifting moment about the center of lift. (This is more fully discussed hereinafter in relation to FIG. 2.) As the bow is lifted, water drag forces are reduced and the boat speed increases.
Although this system is effective, this method possesses several disadvantages. First, as the drive unit is trimmed out, the direction of thrust departs from the direction of boat motion. The result is a loss in useful thrust. Additionally, as the drive unit is trimmed out, a portion of the thrust acts in a downward direction. This adds to the effective weight of the boat and pushes the stern of the boat deeper into the water, thereby increasing water drag forces. Moreover, as the drive unit is trimmed out, the effective pitch of the propeller blades becomes unbalanced. That is, the effective pitch of the blades on the port side is increased with standard propeller rotation, while the effective pitch of the blades on the starboard side is reduced. This results in undesirable steering torque and a drop in propeller efficiency. Finally, the hydraulic trim mechanism is expensive.
Accordingly, it is an object of the present invention to provide an improved method and apparatus for trimming a stern drive or an outboard motor driven boat while minimizing the loss of useful thrust.
It is another object of the present invention to provide an improved method and apparatus for trimming a boat moving in the water while minimizing water drag forces.
Yet a further object of the present invention is to provide an improved method and apparatus for trimming a boat moving in the water without producing unbalanced pitch of the propeller blades, undesirable steering torque, and loss in propeller efficiency.
It is an additional object of the present invention to provide a method and apparatus for trimming a boat moving in the water, where the apparatus is relatively inexpensive.
These and other objects of the invention, as well as the advantages thereof, will become apparent from the following description, when taken in conjunction with the illustrated drawings, in which:
FIG. 1 is a simplified schematic representation shown as a partially cut away side elevational view of an embodiment of the present invention, and,
FIG. 2 is a simplified schematic representation shown as a side elevational view wherein an outboard motor driven boat has a conventional trim system.